Comprehensive study of high-temperature calendar aging on cylinder Li-ion battery

Calendar aging at high temperature is tightly correlated to the performance and safety behavior of lithium-ion batteries. However, the mechanism study in this area rarely focuses on multi-level analysis from cell to electrode. Here, a comprehensive study from centimeter-scale to nanometer-scale on high-temperature aged battery is carried out. After short-time high-temperature aging, measurements of electrochemical performance show notable decay of capacity and increase of internal resistance. The thermal safety behavior is studied through accelerating rate calorimeter (ARC), which indicates that the heat output of the aged battery during thermal runaway is largely increased. The aging mechanism of high temperature is investigated under various scales. Incremental capacity (IC) curves depict the deterioration of electrodes and increase of ohmic resistance. Computational Tomography (CT) reveals structure evolution of aged battery at millimeter scale, indicating gas generation after high-temperature aging. Scanning electron microscope (SEM) shows thickened solid-state-electrolyte (SEI) on anode and cracks on cathode at sub-micrometer scale. X-ray diffraction (XRD) patterns present crystallographic evolution of both anode and cathode. Thus, the cell degradation-mechanism after high-temperature aging is interpreted at multi-level, that high temperature induces deterioration of electrodes, formation of SEI and evolution of gas.